1. Field of the Invention
This invention relates to a power generating apparatus activated by water waves, and, in particular, to a wave-activated power generating apparatus in the form of a buoy suitable for use in shallow waters.
2. Description of the Prior Art
Currently, a wave-activated power generating apparatus is in use as a power source for supplying an electric power for the lamp of a nautical mark buoy. Such a nautical mark buoy typically includes at its center a central pipe extending vertically downward with respect to the water surface, and, utilizing a relative motion between the buoy main body moving up and down following the motion of the waves and the water surface inside of the central pipe, there is produced a forced air flow whose energy is then converted into electric power. In this case, in order to obtain an increased power output, it is required that the above-mentioned relative motion be as large as possible. The movement of each section of the water executing the wave motion resembles a circular motion, but its amplitude decreases rapidly as the depth from the water surface increases. Thus, the longer the vertical length of the central pipe of the power generating apparatus, the larger the relative motion between the buoy main body and the water surface inside the central pipe, so that an increased power output can be obtained. However, if the central pipe is made too longer, there are brought about other disadvantages, such as incapability to be used in shallow waters and difficulty to handle and carry out maintenance operations.